1. Field of the Invention
The present invention relates to an electrophotographic photosensitive member, and more particularly to an electrophotographic photosensitive member without generation of damage and abrasion, and excellent copying durability, a long use life, a small variation in potential characteristics, a high sensitivity and a little generation of residual image phenomenon.
2. Related Background Art
For use in the electrophotographic photosensitive member, there have been proposed various materials such as selenium, cadmium sulfide, zinc oxide, phthalocyanine, amorphous silicon (hereinafter, referred to as "a-Si"). Among these, the non-single-crystalline deposited film containing silicon atoms as a main component which is represented by a-Si, for example, amorphous deposited film such as a-Si film compensated with hydrogen atoms and/or halogen (fluorine, chlorine, or the like) atoms has been proposed as a non-polluting photosensitive member of high performance and high durability, and has already been practically used. Such deposited film can be formed by various known methods, such as sputtering, thermal CVD in which raw material gas is decomposed by heat, photo CVD in which raw material gas is decomposed by light, and plasma CVD in which raw material gas is decomposed by plasma. In particular, the plasma CVD method, in which the raw material gas is decomposed by glow discharge of a DC, high frequency (RF, VHF), microwave or the like to form a thin deposited film on a conductive substrate such as of glass, quartz, heat-resistant plastic film, stainless steel or aluminum, has been significantly developed in the formation of the electrophotographic a-Si deposited film and various apparatus have been proposed therefor.
For example, the Japanese Patent Application Laid-Open No. 57-115551 discloses a photoconductive member including a photoconductive layer of an amorphous material mainly composed of silicon atoms and containing at least either of hydrogen atoms and halogen atoms, and a surface barrier layer formed thereon of an amorphous material composed of silicon and carbon atoms as a matrix and containing hydrogen atoms. Also, the Japanese Patent Application Laid-Open No. 61-219961 discloses an electrophotographic photosensitive member composed of an a-Si based photosensitive layer and a surface protective layer formed thereon of amorphous carbon film (hereinafter, referred to as "a-C:H") containing hydrogen atoms in 10 atomic % to 40 atomic %. The Japanese Patent Application Laid-Open No. 6-317920 discloses a method of utilizing a high frequency of 20 MHz or more and forming an electrophotographic photosensitive member composed of a photoconductive layer of a non-single-crystalline silicon material containing silicon atoms as a matrix and an a-C:H surface protective layer having a hydrogen atom content of 8 atomic % to 45 atomic %. The Japanese Patent Application Laid-Open No. 60-186849 discloses a method and an apparatus for forming an electrophotographic device with a top inhibition layer, by microwave plasma CVD utilizing a microwave (for example, 2.45 GHz) for decomposing a raw material gas.
By utilizing these technologies, the electrophotographic photosensitive member has been improved in the electrical, optical, photoconductive and use ambient characteristics and in durability, and also the improvement in the image quality has been made possible.
In recent years, however, higher image quality and higher speed are required for the electrophotographic apparatus. A higher speed in the electrophotographic apparatus can be achieved by shortening the steps of charging, exposure, development, image transfer and charge elimination. Consequently it is necessary to increase the advancing speed of the copying sheet. In such case, the contact number per unit time and the contact time of the electrophotographic photosensitive member with the copying sheet or with the cleaning mechanism increase drastically. Also the complete cleaning becomes more difficult as the process speed becomes higher. For this reason, the contact force of the cleaning blade to the electrophotographic photosensitive member is generally increased in order to prevent defective cleaning resulting from the vibration of the cleaning blade or the toner escaping under the blade. Therefore, with an increase in the process speed, the photosensitive drum is subjected to a larger frictional force, resulting in physical damages such as frictional damages, or even abrasion of the surface layer which has been entirely intact in the conventional process.
For this reason, there has been desired an electrophotographic photosensitive member that is free from abrasion of the photosensitive member in any high-speed process. Such abrasion becomes more conspicuous when the electrophotographic photosensitive member is made smaller for compactizing the electrophotographic apparatus. For avoiding such damage or abrasion, the outermost surface of the electrophotographic photosensitive member is made harder or more slippery.
As a material meeting such object, a hydrogen-containing amorphous carbon film (hereinafter, referred to as "a-C:H film") is attracting attention. It is considered that a-C:H film, known also as diamond-like carbon (DLC), is an optimum material for the above-described object, because of very high hardness and a specific lubricating property. However, though the a-C:H film has a very high hardness, it shows a high stress in the film and tends to be easily peeled off. For this reason, there has been desired a technology capable of depositing a film of necessary thickness without peeling. Also, the film quality of a semiconductor film needs improvement, in consideration of use in the electrophotographic photosensitive member. More specifically, when the a-C:H film is employed in the surface of the electrophotographic photosensitive member, it often causes adverse effects such as a lowered sensitivity, an increased residual image phenomenon and an increased residual potential.
On the other hand, with increase in the process speed for increasing the speed of the apparatus, the charging ability is lowered because of a shorter charging time. With such decrease of the charging ability, a desired charged potential cannot be obtained unless charged charges are correspondingly increased, and the amount of the photocarriers required for dissipating such increased charges increases inevitably. Therefore, the charging ability and the sensitivity are generally lowered as the process speed becomes higher. For this reason, the improvements in the charging ability and in the sensitivity are more strongly required.
Furthermore, a higher image quality is strongly required for a high-speed electrophotographic apparatus in recent years in addition to a productivity, though the productivity rather than the image quality has been so strongly required for the conventional high-speed electrophotographic apparatus. The electrophotographic photosensitive member using a-Si tends to show the residual image phenomenon in which a previously copied image is thinly copied in a portion of an intermediate density of a next copied image, and the improvement of such residual image phenomenon is strictly required for the higher image quality in recent years.